Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver halide photography. Moreover, this system has advantages over silver halide photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In this dye diffusion transfer recording system, a heat-sensitive transfer sheet containing dyes is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the heat-sensitive transfer sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the heat-sensitive transfer sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, or four colors which consists of the three colors and black, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
In a recording system such a dye diffusion transfer process, it has been known that it is important to impart high heat insulating property to the heat-sensitive transfer image-receiving sheet in order to obtain favorable images.
Thus, for imparting heat insulating property to the heat-sensitive transfer image-receiving sheet, used is a composite support having a microvoid-containing biaxially oriented polyolefin film as a support for the heat-sensitive transfer image-receiving sheet. However, by this method, because of relaxation of the residual stress at the time of stretching by the heat during printing or coating of a receptor layer, the heat-sensitive transfer image-receiving sheet shrinks, causing crinkling and curling.
Aside from this, proposed was installation of a heat insulation layer containing hollow polymer particles for imparting heat insulating property to the heat-sensitive transfer image-receiving sheet (see, e.g., Japanese Patents No. 2541796 and No. 3226167, JP-A-5-8572 (“JP-A” means unexamined published Japanese patent application) and JP-A-2006-88691). However, such a method is not necessarily satisfactory because the following problems have emerged: it is difficult to obtain a uniform and smooth heat-sensitive transfer image-receiving sheet, there arise improper transfer of images, white spots, surface irregularity and protective-layer adhesion failure, the production process is complicated and disadvantageous from the viewpoint of productivity. Further, such a method brings in a new problem that the glossiness of a solid black image deteriorates.
Alternatively proposed is a method of using two or more kinds of latex polymers for the receptor layer (see, for example, JP-A-2007-237643 and JP-A-2007-229987). However, these methods do not necessarily give images having satisfactory properties, for example, in the case where the manufacturing condition or the drying condition is modified in order to improve the productivity of the heat-sensitive transfer image-receiving sheet.
In addition, heat-sensitive transfer image-receiving sheets prepared by aqueous coating often showed, under various environmental conditions (in particular, humidity conditions), difference in properties larger than that of the heat-sensitive transfer image-receiving sheets prepared by organic solvent-based coating. Thus, there has been a demand for reduction of the environmental dependency of the sheets during printing.
Therefore, there exists a need for a method giving images stabilized in properties, even after such modification.